At the beginning of your upkeep, you may return target creature card from your graveyard to the battlefield.
Reya is a mono-white reanimator engine: cheat or ramp her out, survive a turn, then recur a creature from your graveyard every upkeep for free. You stockpile high-impact creatures in the yard, then grind the board with repeatable resurrection while value bombs and stax effects keep opponents from racing you.
Free, repeatable reanimation every upkeep with no mana cost once she's online
Mono-white gives access to the best tutors-by-type, board wipes, and recursion redundancy
Loops well with sacrifice outlets and ETB creatures for inevitable advantage
Flying body that blocks and chips while protecting your engine
Nine mana commander that demands heavy ramp or cheat effects to deploy on curve
Engine only triggers on your upkeep, so she does nothing the turn she lands and is slow against fast combo
Single-target removal or exile on Reya shuts the whole plan down
Mono-white struggles for raw card draw and big mana ramp compared to other colors